M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
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Transcript of M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Investigating Neutrinoless Double Beta Decay
Status of the GERDA ExperimentMichael Altmann
Max-Planck-Institut für Physik, Munich
Physics
Concept
Exp. Setup
R&D DetectorsSchedule, etc.Summary
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Physics Motivation : Nature of the Neutrino
Neutrino masses and lepton flavour mixing established by oscillation experiments
Neutrino mass differences known
Still Unknown: absolute mass values
hierarchy scheme
= anti- ?
Neutrinoless Double Beta Decay
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Physics Goals and Experimental Requirements
For excluding inverted hierarchy:Sensitivity on 10 meV level required ton-scale @ B < 10-4 / keV kg yr
Phase 1
Phase 2
Phase-3
GE
RD
A S
en
sitiv
ity
Klapdor-Kleingrothaus positive evidence
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
GERDA: Germanium Detector Array
Array of HP-Germanium Diodes, made from isotopically enriched (86% in Ge-76) material
Phase-1:Use existing diodes from Heidelberg-Moscow and IGEX ( 15kg)0.01 / keV kg yr intrinsic background expectedGoal: verify concept; probe Klapdor-Kleingrothaus‘ evidence (if no event observed, 1 yr of measuring time needed to disprove at 98% cl)
Phase-2:Increase mass by adding 20 kg of new enriched Ge-detectorsGoal: 100 kg yr statistics at background level B<10-3 / keV kg yr
T1/2 > 2 * 1026 yr meff < 0.09 – 0.29 eV
Phase-3:(Depending on results of phase-2 and possibly other experiments)worldwide collaboration for really big experiment; close contacts and MoU with MAJORANA established
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
GERDA‘s Experimental Concept Assumption: External background is
dominant• Minimize all impure materials close to Ge diodes• Operate Ge diodes in ultraclean environment cryogenic liquid shield (LN or LAr); graded shielding
• Reject remaining background (internal and external) by exploiting different interaction topology (single-site multi-site; PSA)
Goal: Background index of 0.001 cts / (keV kg y) at Q=2039 keV
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
GERDA Location: Gran Sasso National Laboratory (LNGS)
GERDA1400 m ~ 3.800 m.w.e
Assigned Location for Phases 1 & 2: LNGS Hall A, next to the CRESST and LVD Experiments
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
GERDA‘s Cleanroom Facility at LNGS: LArGe
HD-Moscow‘s KI-detectors were handed over to GERDA
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Detector Arrangement
Modular Detector Arrangement :- Detector strings
- Hexagonal string arrangement
- Low mass, low background crystal holders and suspension- Additional strings can „easily“ be added when new detectors become available, with the vessel remaining cold
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Detector Suspension for Phase-1
- Low mass (bgd index < 10-2 / keV kg y )
- Use only screened materials with known radioimpurities (Cu, PTFE, Si)- Specific ORTEC-type contact (bottom of bore hole)- Mount and test every crystal individually (LArGe Facility at LNGS)
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Ge-76 Procurement for Phase-2
- Enrichment of 37.5 kg of Germanium ongoing (ECP, Krasnoyarsk, Russia)
- Delivery procedure tested with natGe: very smooth, no problems encountered (20 day trip Krasnoyarsk Munich, special shielding container: 10-20 attenuation factor for cosmogenic production of 68Ge and 60Co)- ongoing R&D: maintaining original purity during enrichment
optimizing yield of chemical purification to 6N metal
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Phase-2: Segmented DetectorsInteraction topology of -signal and -
background different anticoincidence for bgd suppression„pointlike“, single-site vs. „extended“, multi-site
60Co: 2 photons (=O(cm))
(multiple) Compton-scattering
2 electrons deposit energy locally (d = O(1 mm))
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Detector Development for Phase-2R&D on two types of detectors: p-type and n-type
n-type prototypes: Naked crystal: available & operated in LN Naked crystal, 6x3z segmented, true coax: on orderp-type prototypes:
Naked crystal, true coax: available & operated in LN
Naked crystal, true coax, 6x 1z segmented: available Naked crystal, true coax,
6x 3z segmented: on order
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Detector Suspension for Phase-218-fold segemented
detectors (true-coaxial, 3x6, n-type)
Kapton cable
bonded contacts
Total of 30g mounting material / detector
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Simulation Results on Segmented Detectors
- Monte Carlo (MaGe: common Majorana-Gerda simulation framework) : Anticoincidence between segments (18-fold segmentation)
factor 10 increase in 60Co rejection
- Further improvement (up to factor 5):Analysis of pulse shapes and mirror charges (PSA)( regain signal sitting on segment boundary)( 0.2 cm spatial resolution)
- R&D ongoing: Monte Carlo studies and PSA development Laboratory measurements with prototype
detectors
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Pulse Shape SimulationFull simulation of true coaxial 6-fold segmented detector (only 1 segment hit):
electrode electrode electrode
electrode electrode electrode
core
Cha
rge
Time
Hit segment:full energy deposit
Core signal: full energy deposit
Neighbouring segments:mirror charges
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Full Simulation of a True-Coax 18-fold Segmented Detector
Signals seen by the segment electrodes Position Reconstruction ( and z)
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Simulation Results on Segmented Detectors
PSA Information on radius and angle:
Clear correlation between time of charge collection and radius of interaction point
Correlation between ratio of amplitudes of neighbouring segments and angle of interaction point
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Status & Time Schedule2004:• Feb Letter of Intent to LNGS (hep-ex/0404039)• Sep Formation of Collaboration• Oct Funding request approved by MPG; Proposal to LNGS (wwwgerda.mppmu.mpg.de)
2005:• Feb GERDA approved by LNGS• Mar Technical proposal to LNGS; 30 kg of enriched Ge-76 for phase-2 ordered• May Funding requests approved by INFN• Jun Funding request approved by BMBF• Jul Ge-76 order enlarged to 37.5 kg; safety study for cryostat submitted to LNGS• Aug Expect decision by LNGS on system safety• Sep if OK: tendering for water tank, first orders for cryostat
2006:• Jun Start of water tank installation at LNGS• ??? Installation of cryostat, clean room and lock, muon veto, ...
2007:• spring Commissioning, then start of physics run
M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005
Summary and Conclusions
Approved by LNGS with location in hall A
substantially funded by BMBF,MPG, INFN and Russia (in kind) construction at LNGS start 6/06
in parallel: substantial R&D for and preparation of phase II start of data taking in 2007
phase-1: verify concept, probe KK-evidence for 0phase-2: T1/2 > 2 * 1026 yr m
eff < 0.09 – 0.29 eV phase-3: t.b.d., depending on results; ton-scale experiment in worldwide collaboration